This invention relates in general to motorcycle wheels and in particular to an apparatus and method for casting motorcycle wheels.
One piece motorcycle wheels formed from alloys of light weight metals such as aluminum, magnesium and titanium are becoming increasingly popular. Such wheels can be formed by conventional gravity casting processes which utilize highly automated casting machines. A type of automated casting machine has a plurality of multiple piece wheel molds mounted upon a carrousel. The carrousel is rotationally indexed to move the molds into a charging position where a charge of molten metal is poured into the mold. As the carrousel continues to be indexed, the molten metal cools and solidifies into a wheel casting. The wheel mold is then opened and the casting removed. The mold is reclosed and returned to the charging position. Other types of automated casting machines also can be used. Sprues and risers are removed from the wheel casting and the casting machined to a final shape.
Referring now to FIG. 1, there is shown generally at 10, a typical prior art motorcycle wheel mold. The mold includes a base member 11 which is mounted upon a casting machine carrousel (not shown) and supports the other mold components. The mold 10 also includes a plurality of horizontally movable side members. As shown in FIG. 1, the mold 10 includes a left side member 12 and a right side member 13. The mold 10 further includes a vertically movable cup shaped top core 14. A ball member 15, which has an inverted cup shape, is attached to the upper surface of the center of the top core 14.
As shown in FIG. 1, the side members 12 and 13 and top core 14 are in their extended positions and cooperate to define a mold cavity 20. The mold cavity includes an annular rim cavity 21 connected by a plurality of radial spoke cavities 22 (one shown) to a central hub cavity 23. The ball member 15 defines a ball riser 24 which is adjacent to the upper end of the hub cavity 23. Similarly, an axially extending annular rim riser 25 is formed in the side members 12 and 13 adjacent to the upper end of the rim cavity 21. As shown in FIG. 1 a gate 30 is formed in the right side member 13. The gate 30 includes a conical inlet chamber 31 which receives the molten metal. The inlet chamber 31 communicates through a passageway 32 with an intermediate chamber 33. An axial slot 35 provides communication between the intermediate chamber 33 and the mold cavity 20.
To cast a motorcycle wheel, a charge of molten metal is poured into the gate 30. The molten metal flows into the rim cavity 21 and through the spoke cavities 22 into the hub cavity 23. Additional molten metal is accumulated in the ball riser 24 and the rim riser 25. As the metal in the wheel cavity 20 cools, the metal contracts and gravity causes additional molten metal to flow from the ball and rim risers 24 and 25 into the mold cavity 20. Once the metal has solidified, the top core 14 and ball member 15 are raised and the side members 12 and 13 retracted to allow removal of the wheel casting. The ball and rim risers are cut from the casting and the casting machined to a final shape, which is shown by the dashed outline labeled 37 in FIG. 1. In order to minimize machining, the shape of the rim cavity 21 closely approximates the shape of the finished motorcycle wheel rim.
This invention relates to an improved apparatus and method for casting motorcycle wheels.
Due to the geometry of motorcycle wheels, the wheel rim and spokes have small cross-sectional areas. Accordingly, the metal in the spoke and rim cavities tends to cool more rapidly than the metal in the hub cavity. Referring again to FIG. 1, as explained above, the rim cavity is shaped to closely follow the final rim shape of the wheel. This is done to minimize the amount of machining needed to finish the wheel. However, as the metal in the spoke cavities 22 solidifies, the flow of molten metal from the hub ball riser 24 to the rim cavity 21 is blocked. Similarly, as the metal in the rim cavity 21 solidifies, the flow of molten metal from the rim riser 25 can be blocked. Thus, shrinkage in the rim and spoke cavities 21 and 22 may not be replaced with additional molten metal and might lead to rejection of the wheel casting. Therefore, it would be desirable to provide an improved mold which would assure that additional molten metal can be supplied to the rim and spoke cavities 21 and 22.
The present invention contemplates a mold for casting a motorcycle wheel which includes a base member and a plurality of side members with at least one of the side members including a gate adapted to receive molten metal. The mold also includes a top core and the mold has a central axis. The top core cooperates with the base member and side members to define a mold cavity having an annular portion which defines a rim cavity for casting a motorcycle wheel rim. The mold cavity communicates with the gate formed in the side member. An annular rim riser is formed upon an end of the rim cavity. The rim cavity has a gently undulating outer surface between the annular rim riser and spoke cavities so that there are no more than two changes of direction relative to the mold central axis and the rim cavity has a sufficient width to facilitate the flow of molten metal from the rim riser into the mold cavity. The mold members further define a central hub cavity which communicates with the rim cavity through at least one radial spoke cavity. The central hub cavity communicates with a hub riser.
The invention also contemplates that a slot is formed in the side member, the slot communicating either between the gate and the rim riser cavity or between the gate and the rim cavity. Alternately, a first slot can be formed in the side member which communicates between the gate and the rim riser cavity and a second slot can be formed in the side member which communicates between the gate and the rim cavity.
The invention further contemplates a process for casting a motorcycle wheel which includes providing the motorcycle wheel mold described above. Molten metal is poured into the mold gate, the molten metal filling the rim cavity and flowing through at least one of the wheel spoke cavities fill the central hub cavity. The molten metal is allowed to cool sufficiently to solidify into a motorcycle wheel casting. The mold is then opened and the casting removed.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.